Thermostat



Patented Feb. 7, 1933 CHARLES F. GERMEYER, OF HARRISBURG, PENNSYLVANIA THERMOSTAT Application led March 18, 1930. Serial No. 436,878.

nent magnet and contacts in such a way that the relatively stationary contact and its support act as a keeper to maintain the strength of the magnet, while the movable contact has a small armature which takes only a small proportion of the total flux of the magnet.

The magnetic force actually utilized in this way is sufficiently small to avoid ydestroying the sensitiveness of the device, and a uni- 'forinly good kee'ping7 effect is provided for,

or closed, which is not true of devices in which the only keeper is the armature associated with the movable contact.

Another object is to improve the responsiveness to temperature changes in a room, by constructing the thermostat in such a way that the temperature responsive element will be bathed in a constantly flowing stream of air from the room, that it will 'readily exchange heat with the air, and that it will be protected from radiant heat.

Other objects will appear from the specification which follows.

The invention is illustrated by way of eX- anple in the accompanying drawing, in which e Fig. 1 is a front view of a thermostat casing constructed in accordance with my invention;

Fig. 2 is a section on the line 2-2 of Fig. 1;

Fig. 3 is a front view of the thermostat with the cover removed; and

Fig. 4 is a bottom view of the thermostat.

A base 10 has holes 11 to receive mounting fixtures for securing the thermostat to a regardless of whether the contacts are open' wall.- A lug 12 extends out from the base and is provided near its end with a hole to receive a screw 13 which serves to fix the lower end of a bimetallic temperature responsive element 14 to the lug 12. The element 55 14 and screw 13 are electrically connected by a metallic washer 15, but are insulated from the lug 12 by insulating Washers 16 and an insulating bushing (not shown) around the screw inside the hole in lug 12. A nut 17 30 binds the above parts together and a second nut 18 serves to connect a wire (not shown) to the'scrcw 13 and thus to the element 14. The wire can be led in through hole 19.

At the upper end of the thermostat a per- 05 manent horseshoe magnet 20 is fixed to the base by a screw 21 and nut 22. The magnet shown has a. long pole 23 and a short pole 24 and the screw 21 extends out from the long pole substantially toward the short pole, in this case across the end of the short pole.

A contact disk 25 screwed onto the outer end of screw 21 has a curved edge 26 which forms one of the contact surfaces. To the upper end of element 14 is fixed a curved armature 75 27, in the curved face of which is embedded a tiny rounded contact point 28 protruding very slightly beyond the surface of the armature.- Under the influence of a temperature change in one direction, the element 14 80 will bend and bring the point 28 into 'engagement with the contact face 26, thus closing an electric circuit (not shown).

The side and front walls of the thermostat are formed in one piece which is fixed to the bottom of the base by two screws 29 and to a, bracket 30 at the top by a screw 31. The bracket 30 is conveniently fastened upon screw 21 by nut 22.- Upon the front face of the thermostat is a thermometer 32 and above 90 this a curved slot 33 with a temperature scale 34 along its lower edge. A handle 35 is bent forward at its upper end 36 through the slot 33. The extreme end is pointed and indicates the adjustment of the contact disk on scale 34. The handle 35 is fastened to disk 25 by a screw 37 passing through a slot 38 in the handle, which permits limited adjustment of the handle with respect to the disk. The lower end 39 of the handle is 100 threaded on screw 21 and is sprung out from disk 25 to give an end thrust capable of holding the disk in anyA position in which it is set. The contour of the edge 26 is so designed that equal angular displacements of the disk cause equal radial'displacements of the point on the edge 26 opposite contact point 28.

The screw 21 and contact disk 25 are made of material having low reluctance; consequently they complete a low reluctance path for the magnetic iiux except for a small gap 40 between the contact disk and the short pole of the magnet. This ispractically the case no matter what the position of the contact disk, so that the magnet constantly has the beneit of a keeper to help it to retain its magnetism. Most of the magnetic iux passes from the long pole through the support 21,

20 contact 25, and narrow air gap 40 to the short pole When the armature 27 is moved by the ending of element 14 to' a position where suiicient flux is deiected through it to overv come the tension of element 14, the armature is snapped toward disk 25 and point 28 makes a pcs1tive contact with surface 26. Even at this time, however, only a small proportion of the flux is shunted throu h the armature. Most of it extends directly om the disk 25 3 0 to the pole 24 regardless of the position of the armature 27. When the temperature changes in the opposite direction enough 'to create a tension in element 14 capable of overcoming the magnetic attraction of the 35., armature, the free end of element 14. springs out breakin the circuit and carrying the rlliature sustantially clear of the magnetic The base, side, and front walls of the casing 4 0`are substantially closed, at least when the mounting fixtures have been inserted in holes 11; thus forming a chimney which induces a lively current of air through the casing. The lug 12 is'made as narrow as possible to offer the least obstruction to the air current. The .temperature responsive element 14 is made a dead black to increase its capacity for exchanging heat with the air, while the inner walls of the casing are brightly polished 'to protect the element 14 from radiant heat. The thermostat is thus able to accurately and rapidly respond to the true temperature of the air in a room.

It is essential to my invention to have the contact 25, as well as its support 21, and,

vof course, the armature 27 composed of magnetic material. Furthermore the armature must be able to come very close'to the contact 25, to enable the use of a very weak 50 magnetic flux affecting the armature, in order to secure great sensitiveness. However, magnetic materials do not make good contact surfaces and it is not practical to havethe contact take place directly between the mag- 5 netic armature 27 and the magneticcontact 25. I have found that it is possible toput a thin plate of silver upon the contact 25 without interfering with the magnetic effect' upon the armature. Even the extremely thin film of silver used, say five thousandths of an inch in thickness, will not burn through, as would platinum, for example, because it dssipates the heat very rapidly. I have also found that a ood contact on the armature Aside can be ma e by embedding a tiny rounded point of platinum in the face of the armal ture in such a way that it projects only a few thousandths of an inch above the surface. Platinum is hard enough for this duty and the bulk of the point being relatively large- (compared with the thickness of the plate on contact 25) and the point being embedded in the armature, it is able to dissipate the heat quickly enough.

It will be seen that by turning the lscrew 21 on the base a new line of contact points on the disk 26 canbe brought opposite the point 28, thereby greatly extending the life' of the contact disk.

Various modifications may be made in the illustrative form of the invention-described above, without departing from the scope'of claims.

What I claim is: 1. In a thermostat, a permanent horseshoe the invention as defined in the appended magnet, a contact support mounted on onepole of said magnet, a contact on said support adjacent the other pole of said magnet, said support and Contact being composed of material having low reluctance, thereby forming an essentially closed magnetic circuit, a temperature responsive element having a free end adjacent said contact, an armature and a second contact on the free end of said element, said armature being influenced by leakage flux from said magnetic circuit, 'Y

said second contact adapted to engage said first contact. v

2. Ina thermostat, a permanent horseshoe magnet, a contact support mounted upon one pole of said 'magnet and extending substantially toward the other pole thereof, a con tact eccentrically pivoted on said support adjacent said other pole, so as to be adjustable about an axis transverse to the poles of 'said magnet, said support and contact being composed of material having low reluctance, a

vtemperature responsive element having a free form of a pivoted disk having an eccentrically curved edge, a temperature responsive element having a free end adjacent said ap, an armature and a contact on the free en of 5 said element adapted to move into and substantially out of the influence of the lines of force at said gap as said element moves under the infiuence of temperature changes, said;Y armature having a curved shape substantiall0 1y conforming to the curved edge of said first mentioned contact.

4. A thermostat as recited in claim 3 in which the contact on the free end of said temperature responsive'element is in the form l5 of a tiny point of non-corrosive metal projecting slightly from the curved surface of said armature.

5. A thermostat as recited in claim 3 in which said first mentioned contact is plated 1 with a thin coat of silver.

6. A thermostat as recited in claim 3 in which the contact on the free end of said temperature responsive element is in the form of a tin)1 rounded point of platinum embedded 95 in said armature and projecting slightly from the curved surface thereof.

CHARLES F. GERMEYER. 

